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In recent decades, growing concerns about the increasing atmospheric carbon dioxide (CO2) levels have led to a global push towards the mitigation of anthropogenic CO2 emissions from fossil fuels. Clean coal technologies such as the calcium looping cycle show potential for capturing CO2. In this research, the thermodynamic and kinetic simulations of the CO2 capture process on calcium-based sorbent of calcined dolomite were investigated using Aspen Plus software. Furthermore, the performance of dolomite was compared with that of Cadomin limestone in the temperature range of 600-750°C. The experimental data and model results both illustrated a shift in the reaction mechanism with respect to temperature at 650°C.
Novel mixed catalyst-sorbent pellets were prepared with different contents of potassium carbonate and calcium oxide as the catalyst and sorbent, respectively. Experiments were performed on the steam gasification of two different types of coal with these pellets in a fixed-bed reactor. Boundary Dam lignite coal (low-rank coal) demonstrated a higher reactivity than the Genesee subbituminous coal (medium rank). A maximum hydrogen fraction of 80% (dry basis with nitrogen) was obtained from steam gasification of lignite using composite pellets with 50% catalyst at 700°C.
A modified catalytic hydrogen production reaction integrated novel gasification (M-HyPr-RING) process was then developed for high-purity hydrogen production from the steam gasification of ash-free coal. The steam gasification experiments were conducted in the same reactor with different catalyst loadings with and without sorbent. A maximum hydrogen molar fraction of 85% was observed with 20wt% catalyst and a calcium oxide to carbon ratio of 2 at 675°C under nearly atmospheric pressure.
High-purity hydrogen production from the steam-only gasification of woody biomass integrated with CO2 capture was also explored through process simulation in Aspen Plus software, in order to determine the effect of CO2 capture on gasification at a demonstration plant scale. The model was validated with experimental data available in the literature, and a reversible carbonation/calcination reaction of calcium oxide with CO2 was added. The CO2 capture was predicted to enhance hydrogen purity, which in turn improved the higher heating values by 3 times and the cold gas efficiency by 28%.